Avalanche Forecast
Issued: Dec 20th, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Persistent Slabs and Storm Slabs.
mconlan,
Avalanche Canada
An incoming storm will likely cause an avalanche cycle to occur by Tuesday morning. Expect the likelihood of triggering large avalanches to increase as the day progresses. Be conservative and step away from avalanche terrain if you find more than 25 cm of snow accumulation.
Summary
Confidence
Weather Forecast
SUNDAY NIGHT: Partly cloudy, 30 km/h northwest wind, alpine temperature -6 C, freezing level 1000 m.
MONDAY: Snow, accumulation 10 to 20 cm, 30 to 50 km/h south wind, alpine temperature -7 C.
TUESDAY: Early-morning snowfall then clearing, accumulation 20 to 40 cm, 30 to 60 km/h northwest wind, alpine temperature -2 C dropping to -6 C by morning, freezing level 1500 m dropping to 1000 m.
WEDNESDAY: Clear skies, 10 to 20 km/h west wind, alpine temperature -4 C.
Avalanche Summary
Numerous large persistent slab avalanches were triggered by skiers and explosives on Saturday Sunday. They released on the weak layer described in the snowpack summary. They were on all aspects and at an elevation around 2100 m. See this MIN for a great example of what people are seeing in the region.
Snowpack Summary
A hefty storm is forecast for the region from Monday morning to Tuesday morning. Around 10 to 20 cm is forecast for Monday to 4 PM followed by another 20 to 40 cm Monday night, with associated strong south to southwest wind. Expect storm and wind slabs to form over the day as the snow accumulates.
This snow will continue to load a weak layer around 30 to 60 cm deep. The layer may be composed of feathery surface hoar or sugary faceted grains and it overlies a hard melt-freeze crust. Riders have reported substantial avalanche activity and whumpfing on this layer as well as surprising snowpack test results. This layer remains a major concern, as humans may be able to trigger large and destructive avalanches on it.
Another crust with associated faceted grains may be found near the base of the snowpack. There have been no recent avalanches reported on this layer but it remains on our radar. The most likely place to trigger it would be from shallow, rocky terrain.
Terrain and Travel
- Travel in alpine terrain is not recommended.
- Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
- Make conservative terrain choices and avoid overhead hazard.
- Avalanche hazard is expected to to increase througout the day, think carefully about your egress.
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Fresh snow rests on a problematic persistent slab, don't let good riding lure you into complacency.
Problems
Persistent Slabs
A weak layer of surface hoar and/or faceted grains overly a hard melt-freeze crust around 30 to 60 cm deep. The likelihood of triggering this layer will increase as Monday's storm loads it. An avalanche cycle is expected to occur on it by Tuesday morning, likely during periods of rapid snow loading. Riders have already triggered large avalanches on this layer, and the consequence of doing so will only increase as it gets deeper.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Storm Slabs
A powerful storm will cross the region Monday and Monday night. Snowfall totals by Monday 4 PM are expected to be 10 to 20 cm, with another 20 to 40 cm expected Monday night. Storm and wind slabs will build over the day and will likely be reactive to riders.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Dec 21st, 2020 4:00PM
